1. Field of the Invention
The present invention relates to a video information processing apparatus and a video information processing method both of which convert interlaced video information into progressive video information in television.
2. Description of the Related Art
In recent years, the transition from existing analog television systems to digital television systems has started to be considered. Owing to new technological innovations called digitization, television broadcasting is growing into to a far advanced information communications medium, and is making far more rapid progress. In Japan as well, digitization has already been realized in broadcasting using a CS (Communication Satellite) and broadcasting using a BS (Broadcasting Satellite). In addition, digitization of ground-wave broadcasting is currently being considered, and in the near future, all broadcasting waves will change to digital waves.
A great merit of digital television broadcasting is that a digital system can transmit three channels of programs with a frequency band corresponding to one channel in an analog system, so that multiple channels can be provided. Accordingly, it is possible to realized new services such as multiple programs (mixed multiple organized programs) in which news, sports, dramas and the like are combined, and multi-channel broadcasting in which three different programs are broadcasted in one channel.
Furthermore, digital television broadcasting enables broadcasting of not only video and audio but also integrated broadcasting services containing various kinds of data broadcasting. Services containing various kinds of data broadcasting are divided into types which provide multimedia-like services by adding data information to television programs and types which provide services independent of television programs. As main services, audience-participation programs, home shopping, various information services, and weather forecasts and news which can be watched at any time.
To cope with this digital television broadcasting, receivers for television broadcasting are also making progress, and flat-panel large-sized plasma displays have been provided. In addition, existing cathode-ray tube types of television receivers having high-definition resolution for digital television broadcasting have been provided. In these display devices, video display is performed not by existing interlaced scanning which scans every other line, but by progressive scanning. Accordingly, in the case where an existing analog television broadcast is displayed, interlaced video information is converted into progressive video information (hereinafter referred to as IP (Interlace-Progressive) conversion), and the resolution of the video information is converted to the resolution of a display device so that the video information is visually displayed.
The following is a brief description of a related-art IP conversion processing circuit. FIG. 9 is a block diagram showing the construction or a related-art general IP conversion processing circuit In FIG. 9, reference numerals 101 and 102 denote field information storage units which store inputted video information in units of fields. Reference numeral 103 denotes a motion detector-generator. This motion detector-generator 103 finds the difference between the currently inputted field information and field information which is outputted from the field information storage unit 102 and was inputted one frame period previously to the currently inputted field information, thereby determining in units of pixels whether the input video information is moving-image information or still-image information. Furthermore, the motion detector-generator 103 determines the motion of an interpolation pixel, from the obtained motion information on each pixel, and outputs the determined motion.
Reference numeral 104 denotes a line information storage unit which stores the inputted video information in units of lines. Reference numeral 107 denotes an adder which performs addition on two inputted signals Reference numeral 108 denotes a divider which finds the half value of the sum of values added by the adder 107. Reference numeral 109 denotes an interpolation information selecting unit. The interpolation information selecting unit 109 selects, according to the output signal from the motion detector-generator 103, either pixel information which is outputted from the field information storage unit 101 and was inputted one field period previously to the currently inputted field information, or an average value of pixel values which is outputted from the divider 108 and contained in lines above and below an interpolation pixel position, and determines the selected information as an interpolation pixel value.
Reference numeral 105 denotes an input-output conversion speed unit for storing the pixel information outputted from the interpolation information selecting unit 109 in units of lines and reading out the stored pixel information at a speed twice that of the inputted video information, while reference numeral 106 denotes an input-output conversion speed unit for storing the inputted pixel information in units of lines and reading out the stored pixel information at a speed twice that of the inputted video information. Reference numeral 110 denotes a display information selecting unit which outputs pixel information while effecting line-by-line switching between the pixel information outputted from the input-output conversion speed unit 105 and the pixel information outputted from the input-output conversion speed unit 106.
The operation of the related-art IP conversion processing circuit will be described below. Inputted interlaced video information is inputted to the field information storage unit 101 and to the line information storage unit 104, and pixel information which is delayed by one field period is obtained from the field information storage unit 101, while pixel information which was inputted one line previously is obtained from the line information storage unit 104.
FIGS. 10A to 10C are views showing video information displayed by interlace scanning of the NTSC (national television system committee) signal. In FIG. 10A, in the NTSC signal, one picture is made of 525 horizontal lines, and the unit of this one picture is called a frame. The frame is divided into an odd field in which odd lines are represented by interlace scanning as shown in FIG. 10B and an even field in which even lines are represented by interlace scanning as shown in FIG. 10C. In the NTSC signal, 525 lines of video information are represented by alternately displaying the odd field of video and the even field of video. Namely, the odd field and the even field are in the relationship of mutual interpolation of their shortages of line information.
Accordingly, the previous field of pixel information corresponding to the position of a pixel to be interpolated is obtained from the field information storage unit 101. In addition, pixel information contained in lines above and below the pixel to be interpolated is obtained from the inputted video information as well as from the line information storage unit 104. Furthermore, the average value of the pixel information contained in the lines above and below the pixel to be interpolated is found from the inputted video information and the line information storage unit 104 by the adder 107 and the divider 108, and is used as interpolation pixel information for a moving image.
The pixel information outputted from the field information storage unit 101 is further one field period delayed by the field information storage unit 102, whereby video information delayed by one frame period from the inputted video information, i.e., pixel information contained in the previous frame corresponding to the position of the inputted pixel is obtained.
The motion detector-generator 103 will be described below. FIG. 11 is a block diagram showing the construction of the motion detector-generator 103. In FIG. 11, reference numeral 1031 denotes a subtracter which finds the difference between the currently inputted field information and the field information which is outputted from the field information storage unit 102 and was inputted one frame period previously to the currently inputted field information.
Reference numeral 1032 denotes an absolute-value unit which finds the absolute value of the difference value found by the subtracter 1031. Reference numeral 1033 denotes a threshold filter circuit which compares the value found by the absolute-value unit 1032 and a preset threshold. If the value found by the absolute-value unit 1032 is smaller than the threshold, the threshold filter circuit 1033 determines that the pixel is a still-image pixel, and outputs the value “0”. On the other hand, if the value found by the absolute-value unit 1032 is greater than or equal to the threshold, the threshold filter circuit 1033 determines that the pixel is a moving-image pixel, and output the value “1”. Accordingly, even if invalid pixel information such as noise is added to the inputted video information, the threshold filter circuit 1033 can eliminate the influence as long as the invalid pixel information is a small variation.
Reference numeral 1034 denotes a line motion information storage unit which stores in units of lines motion information on each pixel outputted from the threshold filter circuit 1033. Motion information on a pixel which was inputted one line previously to the inputted video information can be obtained from the line motion information storage unit 1034.
Reference numeral 1035 denotes a two-input one-output OR element which finds the logical sum of the motion information outputted from the threshold filter circuit 1033 and the motion information on the pixel which is one line previous and is outputted from the line motion information storage unit 1034, thereby determining motion information on an interpolation pixel and outputting the motion information.
If the motion information outputted from the motion detector-generator 103 is the value “0”, the interpolation information selecting unit 109 selects the pixel information outputted from the field information storage unit 101, whereas in the case of the value “1”, the interpolation information selecting unit 109 selects the pixel information outputted from the divider 108 and outputs the pixel information as interpolation pixel information.
The input-output conversion speed unit 105 and the input-output conversion speed unit 106 respectively store in units of lines the interpolation pixel information outputted from the interpolation information selecting unit 109 and the inputted video information. The stored pixel information is read at a speed twice that of the inputted video information, and the display information selecting unit 110 outputs the pixel information while effecting line-by-line switching between the pixel information outputted from the input-output conversion speed unit 105 and the pixel information outputted from the input-output conversion speed unit 106.
However, in the above-mentioned related-art IP conversion method, since the difference information between frames is used for the detection of motion information, if a motion occurs in a field between frames, the moving image is determined as a still image, so that erroneous data is set as an interpolation pixel value.
In addition, in the case where invalid pixel information is added by the influence of noise and the like and motion information cannot be accurately detected, switching frequently occurs between interpolation pixel information indicative of a moving image and interpolation pixel information indicative of a still image, so that a remarkable image quality degradation occurs in video.
To cope with these problems, several proposals have already been made. For example, to solve the erroneous detection caused when a motion occurs in a field between frames, JP-B-8-32025 and JP-A-2000-175159 disclose means for referring to motion information on the previous field as well. In addition, to solve the erroneous detection due to the influence of noise and the like, JP-A-10-98692 discloses means for referring to motion information on the previous frame as well. This method of referring to motion information on a previous field or frame in this manner is means useful for preventing erroneous detection of motion information.
However, as in the case of the above-mentioned related arts, only if motion information on a previous field or frame is simply referred to, new erroneous detection is likely to be incurred. The following is a description of such a case.
FIGS. 12A to 12D are views showing an example in which the letter “H” is displayed while travelling in the horizontal direction from right to left. FIG. 12A shows the display state of video information on a field of interest, FIG. 12B shows the display state of video information on a field which is one field period previous to the field shown in FIG. 12A, FIG. 12C shows the display state of video information on a field which is another one field period previous to the field shown in FIG. 12A, and FIG. 12D shows the display state of video information on a field which is yet another one field period previous to the field shown in FIG. 12A.
In the related-art motion detection method, since motion information is detected by finding the difference between frames, motion information indicative of the display state of FIG. 12A is obtained by comparing the display state of FIG. 12A and the display state of FIG. 12C. FIGS. 13E to 13G are views motion information in individual fields. Consequently, as shown in. FIG. 13E, the display state of “H” shown in FIG. 12A and the display state of “H” shown in FIG. 12C are obtained as motion information.
Similarly, the motion information indicative of the display state of FIG. 12B which corresponds to the field which is one field period previous results as shown in FIG. 13F. Motion information on the next to the field shown in FIG. 12A results as shown in FIG. 13G. In this method, since the motion information is detected between frames, the motion information on the field of interest lacks, as shown in FIG. 13E, the motion information indicative of the display state of FIG. 12B which corresponds to a field between frames.
For this reason, as disclosed in JP-B-8-32025 and JP-A-2000-175159, motion information on the previous field, i.e., the motion information shown in FIG. 13F is also used as the motion information indicative of the display state shown in FIG. 12A, whereby it is possible to avoid this detection leakage. As mentioned above, to refer to motion information in the previous field as well is means useful in preventing erroneous detection of motion information.
However, the motion information necessary for the display state shown in FIG. 12A is information indicating at which location the state of a pixel has varied from the display state which is one frame period previous. Namely, the variations of the motion shown in FIGS. 12A to 12C need only be detected. However, if the motion information shown in FIG. 13F, which is motion information which is one field period previous, is used without modification, motion information which is three field periods previous, i.e., the motion information indicative of the display state of FIG. 12D, will be contained. Consequently, a portion which should be processed as a still image is processed as a moving image.
In the above-mentioned related-art IP conversion method, if that portion is processed as a moving image, an average value of pixel values positioned lines above and below in the same field is found as an interpolation pixel value, so that there is the disadvantage that the vertical spatial frequency is reduced to half, resulting in unsharp video images. For this reason, in order to maintain the vertical spatial frequency, it is preferable to process the portion as a still image as positively as possible and use a pixel value of the previous field as an interpolation pixel value. From this point of view, even when motion information on the previous field is to be used, the avoidance of use of motion information relative to unnecessary motion will lead to prevention of degradation of image quality.
FIGS. 14H to 14k are views showing an example in which the letter “H” is displayed while travelling in the horizontal direction from right to left. FIG. 14H shows the display state of video information on a field of interest, FIG. 14I shows the display state of video information on a field which is one field period previous to the field shown in FIG. 14H, FIG. 14J shows the display state of video information on a field which is another one field period previous to the field shown in FIG. 14H, and FIG. 14K shows the display state of video information on a field which is yet another one field period previous to the field shown in FIG. 14H
If the related-art motion detection method is used for these display states, motion information indicative of the display state of FIG. 14H is obtained by comparing the display state of FIG. 14H and the display state of FIG. 14J. Consequently, the motion information shown in FIG. 15M is found. FIGS. 15M to 15Q are views showing motion information on individual fields.
In the case of these display states, referring to the state of the letter which has traveled from the display state of FIG. 14J to the display state of FIG. 14H, an overlapping portion exists between the position of the letter “H” in the display state of FIG. 14J and the position of the letter “H” in the display state of FIG. 14H, and motion information on the overlapping portion is handled as a still image. Although this portion in which the overlap of the letters has occurred must be originally handled as a moving image, the motion information is erroneously detected. Similarly, motion information indicative of the display state of FIG. 14I which is one field period previous results as shown in FIG. 15N.
In this case, erroneous detection information is contained in the motion information itself, so that accurate motion information on an interpolation pixel cannot be found. Furthermore, if motion information containing this erroneous detection information is used as motion information on the previous field as mentioned above in connection with FIGS. 12A to 13G, it becomes impossible to completely remedy erroneous detection. Accordingly, if more accurate motion information on an interpolation pixel is to be found, it is necessary to take measures against erroneous detection such as those shown in FIGS. 14H to 15Q and use the obtained information as motion information on the previous field. This erroneous detection cannot be avoided merely by referring to motion information on previous fields such as those shown in FIGS. 12A to 13G.
In the above description, reference has been made to the fact that erroneous detection of motion information which is caused by finding difference information between frames cannot be solved by simply referring to moving image on previous fields. However, even in the case where motion information on previous frames are referred to in order to reduce the influence of noise and the like, if similar erroneous detection information is contained in the motion information on the previous frames, no sufficient effect can be expected.